a) Field of the Invention
The invention concerns an automatic choke system for carburetors provided on engines installed in motorcycles, motor scooters, etc.
b) Description of Related Art
A conventional automatic choke system for a carburetor installed on an engine, as is widely known, increases the fuel-to-air ratio at low engine operating temperatures in order to ease starting the engine smoothly. Subsequently, the choke system automatically returns; the fuel-to-air ratio to normal (as specified), and establishes the proper rate of engine rotation upon a corresponding rise in the operating temperature of the engine.
Specifically, a throttle valve in the carburetor is regulated by an accelerator pedal, etc. to control the flow of fuel/air mixture in a main air passageway. A starter valve provided in a passageway by-passing the main air passageway and a needle provided in an auxiliary fuel passageway connected with the by-pass passageway are opened automatically at low temperatures of the engine, thereby providing an increased fuel-to-air ratio.
When the engine reaches a predetermined operating temperature, the starter valve closes the by-pass passageway and the needle also closes the auxiliary fuel passageway, automatically returning the fuel-to-air ratio to normal and establishing the proper rate of engine revolution.
FIG. 7 shows a conventional carburetor with a main body 20 comprising a main air passageway 21, a by-pass passageway 22 by-passing the main air passageway 21, and an auxiliary fuel passageway 24 connected with the by-pass passageway 22. A throttle valve 23 is provided in the main air passageway 21. A starter valve 25 and a needle 26 form the automatic choke system 34 for automatically opening the by-pass passageway 22 and auxiliary fuel passageway 24 when the engine is at low operating temperatures, and closing these when the temperature is elevated.
The FIG. 7 does not show a main fuel passageway connected to the main air passageway 21, however, this is well known in the prior art.
The starter valve 25 and needle 26 are mounted on the tip end of a moving part 28. The moving part 28 is pushed by piston 27a of a thermo-element 27 and a return spring 30 pushes back on the moving part 28. The thermo-element 27, piston 27a and the moving part 28 are housed in a case 29. A thermistor 31 is adhered to the thermally expanding wax side of the thermo-element 27, as set out hereunder, to limit an electric current with an increase in the electric resistance due to the heat generated by the electric current. Wiring 32 links the thermistor 31 with a connector 33 for further connection with an electric circuit (not shown).
FIG. 8 is a cutaway detail drawing of the thermo-element 27 including thermally expanding and contracting wax 27b made from paraffine and copper powder housed in a case 27c. A guide tube 27f is coupled to the opening of the case 27c and houses a fluid 27e. The thermal wax 27b and the fluid 27e are contained and separated from one another by means of a diaphragm 27d made from nitrile rubber, etc. A piston 27a is movably inserted into guide tube 27f with a gasket 27g provided between the guide tube 27f and the piston 27a. A back-up ring 27h is surrounded by the gasket 27g, the guide tube 27f and the piston 27a. Bushings 27i are provided between the guide tube 27f and the piston 27a to guide movement of the piston 27a.
FIG. 9 is a side view showing the automatic choke system 34 installed on the top surface 20a of the carburetor main body 20. Thermally insulating cover 40 is provide over the automatic choke system 34. FIG. 10 is a partial side view of a motorcycle or a motor-scooter 35 with an engine 36 on which a carburetor main body 20 equipped with the automatic choke system 34 is installed. An air cleaner 37 is also installed on the main body 20 of the carburetor.
The conventional automatic choke system 34 is arranged, in linear sequential order, with the needle 26, the starter valve 25, the moving part 28, the thermo-element 27 and the thermistor 31, all housed in the case 29. As shown in FIG. 9, the automatic choke system 34 is substantially elongated and is mounted on the top surface 20a of the carburetor main body 20 with the thermally insulating cover 40 covering the top of the automatic choke system 34.
One problem with conventional arrangements is that a relatively extensive space must be secured above the carburetor main body 20. In addition, when the engine 36 is equipped with the elongated automatic choke system 34 underneath seat 38, the compartment 39 of the motorcycle or motor-scooter 35 cannot be used for storing a helmet or anything else because the tall automatic choke system 34 restricts the size of the compartment 39. Further, since it was not previously known to make a carburetor main body 20 equipped with an automatic choke system 34 into a more compact unit, the freedom to design a more compact motorcycle or motor-scooter 35 was substantially limited.
Another problem encountered in conventional systems is that if the thermal insulation of the thermo-element 27 for the automatic choke system 34 is poor, the thermally expanding wax 27b in the thermo-element 27 remains contracted. The starter valve 25 and the needle 26 of the automatic choke system 34 also respectively keep the by-pass passageway 22 and the auxiliary fuel passageway 24 open, hence the engine cannot be easily restarted a few minutes after the engine is turned off, but is still warm.